1. Field of the Invention
The invention relates to a method and device for motion estimation, a motion-compensated picture signal processing device comprising such a motion estimation device, and a picture display apparatus comprising such a motion-compensated picture signal processing device.
2. Description of the Related Art
A prior art motion estimation technique, called “3-D Recursive Search”, has been described by Gerard de Haan and Robert Jan Schutten, “Real-time 2–3 pull-down elimination applying motion estimation/compensation in a programmable device”, IEEE Transactions on Consumer Electronics, Vol. 44, No. 3, August 1988, pp. 930–938. 3-D Recursive Search falls in the class of pixel- or block-recursive motion estimators. The algorithm is based in the following assumptions: motion does not change much in time, i.e., from frame to frame. The algorithm maintains a motion field and tries to update this field only when necessary. The motion field is usually similar for a relatively large region, i.e., for an object. Therefore the motion vectors in the neighborhood of a location are good candidates for the motion in that location. Video consists of a sequence of frames. Each frame is divided into blocks, e.g., of 16×16 pixels. A motion vector is associated with each block. The motion vector should hold the displacement between the block in the current frame compared to the previous frame. Suppose that we want to update the motion vector of block (x,y) in the current frame. 3-D Recursive Search uses only a limited number of candidate vectors, say five, for the estimation, viz. some vectors from the previous frame, i.e.) temporal vectors, some vectors from the current frame, i.e., spatial vectors, and an update of a spatial vector. For each candidate the motion estimation error is calculated. The candidate with the lowest motion estimation error is chosen as the best motion vector for that block. The algorithm uses the normal raster scan order to go through the blocks.
International Patent Application No. WO-A-97/46,022, corresponding to U.S. patent application Ser. No. 08/863,700, filed May 27, 1997, discloses a method of estimating motion vectors, in which motion parameters are determined for a given field of a video signal, and motion vectors for a subsequent field of the video signal are determined in dependence upon at least one predetermined motion vector (i.e., a motion vector already estimated for a spatio-temporally neighboring block) and at least one additional motion vector derived from the motion parameters. The motion parameters for the given field may be derived from motion vectors determined for the given field, e.g., by applying a two-dimensional histogram operation on the motion vectors determined for the given field.
European Patent Application EP-A-0,652,678, corresponding to U.S. Pat. No. 5,473,379, discloses a method and apparatus for improving a block-based motion compensation in digital video coding. The location of the search window within a reference frame is defined using the global motion of the frame. In one embodiment, the global motion vector is generated utilizing the motion vector occurring with the most repetition within a plurality of previously stored motion vectors.